Elevated storage tank



Jan. 16, 1968 R. STUART 'ELEVATED STORAGE TANK Filed Dec. 6) 1965 1NVENTOR. AEECE STU/1R7, E BY ATTO/P/VEVS.

United States Patent 3,363,795 ELEVATED STORAGE TANK Reece Stuart III,Des Moines, Iowa, assignor to Pittsburgh-Des Moines Steel Company, acorporation of Pennsylvania Filed Dec. 6, 1965, Ser. No. 511,884 6Claims. (Cl. 220-1) ABSTRACT OF THE DISCLOSURE This invention relates toan elevated storage tank for use as a water reservoir and, moreparticularly, to such a tank having a vertical column supported by theground and a storage shell surrounding the upper portion of the columnand supported solely thereby. In accordance with the present invention,the storage tank includes a tubular vertical column, the upper part ofwhich is surrounded by a shell having its top and bottom edges attachedto spaced circumferences of the column and solely supported thereby. Theshell has a plurality of vertically defined zones that progressivelyincrease in curvature from top to bottom along a line defined by theintersection of the shell and a vertical plane containing the axis ofthe column.

It is among the objects of the present invention to provide an elevatedstorage tank of the type described, in which substantially the entireshell structure (except at the extreme top and bottom where the shell isattached to the column and local bending forces are involved) may bemade of relatively thin metal plates, the thickness of which isdetermined solely by the tension stresses involved. In other words, theshell structure is so designed as to eliminate any compression stressesthat are of such a magnitude as to require that the plates be madethicker to prevent elastic buckling.

The foregoing and other objects will be apparent from the followingdescription of a preferred embodiment of the invention, in connectionwith the attached drawings, in which FIG. 1 is an elevation of thestorage tank; and

FIG. 2 is a fragmentary, vertical section of the tank shown in FIG. 1.

The present invention is predicated on the discovery that the objects ofthe invention can be attained by designing the shell portion of thestorage tank, where the water or other liquid is actually stored, sothat the shell will have a certain defined shape that is a modificationof the shape assumed by an elastic membrane when filled with liquid andsupported at top and bottom, respectively, from upper and lowercircumferences of the upper portion of a vertical column. Because a pureelastic membrane, having no compressive strength, would assume acomplicated shape that would not be commercially economical to make, theshell of the present invention represents a practical modification ofsuch an ideal shape.

Referring to the drawings, the elevated storage tank includes asubstantially cylindrical tubular column 1 having a flared base 2resting on a base ring 3. The latter is adapted to be secured tofoundations (not shown) in the ground. Surrounding the upper portion ofthe column is a shell 4, which is wholly supported by the column and isconnected thereto along the top and bottom edges of the shell. The shellis composed of three vertically defined sections or zones. From top tobottom they are a first or upper zone 6 in the form of a frustum of acone, a second or central zone 7 in the form of a section of a sphere,-and a third or bottom zone 8 in the form of a toroidal section. Theshell is made of metal plates that are welded together.

3,363,795 Patented Jan. 16, 1968 The first or upper zone 6 extendsdownwards and outwards, preferably at a slope of around 45 degrees,although the slope may vary for different designs, and terminatesslightly above the level of the maximum height of liquid normallypresent in the tank, as controlled, for example, by an overflow pipe(not shown). The second or central zone 7 is tangent to the upper zone 6and is welded along its top edge to the bottom edge of the upper zone toform the seam 9. The central zone is likewise tangent to the third orlower zone 8 and is welded along its bottom edge to the top edge of thelower zone to form the seam 11. Preferably, the column 1 is reinforcedby a heavier plate or ring 12 in the region where the bottom edge of theshell is attached to the column.

The three zones of the shell may be defined as surfaces of revolutiongenerated by revolving a given line around the axis of the column. Inthe illustrated embodiment, that line corresponds generally to theelevation profile of the shell, which is generally characterized by 1) astraight line segment 13 that generates the upper conical frustum zone6; (2) a first arcuate segment 14 having a radius R1 equal to the planradius of the tank with its center 15 on the axis of the column, whichgenerates the central spherical zone 7; and (3) a second arcuate segment1'6 having a shorter radius R2 with its center 17 on the wall of thecolumn, which generates the lower toroidal zone 8. It will be noted thatthe surface of this last zone where it meets the wall of the column issubstantially perpendicular thereto.

The top of the column 1 is preferably fitted with a circular top plate18, which may be provided with a manhole 19 and a removable cover 21.Similar openings are provided in the column walls at suitable locations,as shown in the drawings; and fixed ladders 22 are mounted inside thecolumn and shell to permit service and maintenance personnel to gainaccess to all parts of the structure. An inlet pipe 23 extends from thebottom of the shell to below grade, where it is connected to suitablepumping and distribution lines (not shown). The pipe is preferablycovered with suitable insulating material 24.

It is among the advantages of the present invention that, in the shellportion of the tank, the governing design stresses are predominantlytensile. As a result, the shell is essentially a membrane, the thicknessof which does not have to be governed by consideration of elasticbuckling loads from compression stresses. Conversely, the center columncan carry the compression load efliciently, because its comparativelysmall radius of curvature can resist high compression stresses withoutdanger of elastic buckling. Such construction permits a considerablesaving in material, or a larger capacity tank at lower cost. A furtheradvantage is that the shell can be substantially assembled around thecolumn at or shortly above ground level, thereby eliminating the needfor extensive and costly scaffolding; and the assembled shell can thenbe raised to the top of the column by using the column as an erectionmast.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

I claim:

1. An elevated tank for the storage of liquid under substantiallyatmospheric pressure, comprising a tubular vertical column, and a shellsurrounding the upper part of the column and having its top and bottomedges attached thereto and being solely supported thereby, the shellhaving a plurality of vertically defined zones that progressivelyincrease in curvature from the top to the bottom of the 3 shell along aline defined by the intersection of the shell and a vertical planecontaining the axis of the column, said zones including from top tobottom a frustu'm of a cone, a spherical section, and a toroidalsection.

2. Apparatus according to claim 1, in which the slope of the conefrustum is around 45 degrees.

3. Apparatus according to claim 1, in which the maximum height of liquidin the tank does not rise substantially above the bottom of the frustumof the cone.

4. Apparatus according to claim 1, in which the column is generallycylindrical in cross section.

5. Apparatus according to claim 1, in which the portion of said linethat lies within the frusto-conical zone is tangent to the adjacentportion of said line that lies in the spherical zone, and in which thoseportions of said line lying in the spherical and toroidal zones meet ata point 4 at which a single straight line can be drawn tangent to bothsaid portions.

6. Apparatus according to claim 5, in which that portion of said linelying in the toroidal zone and constituting a circular arc has thecenter of said are on the surface of the column.

References Cited UNITED STATES PATENTS 73 8, 148 2/1905 Snow 220-11,622,787 3/1927 Horton 2201 1,947,515 2/ 1934 Blackburn 220-1 2,264,66812/ 1941 Horton 220-1 2,657,819 11/1953 Blackburn 220-1 RAEHAEL H.SCHWARTZ, Primary Examiner.

